There are a few more missions in the fluidic space sector which is next to borg space. Then, recently, there have been the weekly Breen episodes located in Oreilus sector. Look on your galaxy map to see the best way to access those sectors. There should be another set of weekly episodes which are set to begin some time this month.

Infected and terradome are STF's (Special Task Force missions). They are designed for a team of 5 players (bridge officers not allowed), and are the most challenging missions in STO. A lot of people say they are too hard, but once you know what to do, they can be fun. Infected is part of a story arc, so once you complete it, there is The Cure, and then Khitomer Accord (in which you can get a sci borg BO btw). All these are 5-man missions. They can be difficult with a pick-up group, but with a fleet, they are definitely doable.